Paper supercalender stack



1 Sept. 12, 1967 P. J. LINK PAPER SUPERCALENDER STA CK Filed Nov. 25, 1964 United States Patent Ofiice 3,340,796 Patented Sept. 12, 1967 3,340,796 PAPER SUPERCALENDER STACK Peter J. Link, Neenah, Wis., assignor to Kimberly-Clark Corporation, Neenah, Wis., a corporation of Delaware Filed Nov. 25, 1964, Ser. No. 413,717 1 Claim. (Cl. 100-162) The present invention relates to papermaking machines and more particularly to the portions of such machines known as calenders or calender stacks. More particularly the invention relates to supercalenders, that is, those calenders including rolls having peripheral surfaces of relatively soft material such as compacted wool, cotton, asbestos, synthetic fibers or mixtures of these materials.

A calender has as its main purposes the compaction to some extent of a paper web and providing the paper with a fine smooth finish, the latter effect being obtained on both sides of the paper by the use of pressure and friction. A conventional calender comprises a plurality of vertically aligned rolls, and the lowermost or king roll of the stack is driven mechanically. The bottom roll drives the roll immediately thereabove by friction, and each lower roll in turn frictionally drives the roll immediately above it. There is some slip between the rolls, and a substantial amount of friction thereby results with respect to the paper as the paper passes through the nips between the rolls.

Alternate ones of the calender rolls are made of polished, fine grain chilled cast iron or hardened steel, and the other rolls are provided with a composition surface, such as compacted wool, cotton or asbestos. The weight of the rolls, usually augmented by additional force, causes an indentation in each composition roll resulting in a speed differential between the nipped surfaces of the metal rolls and composition rolls. The paper web is directed first to the top roll of the stack, and it passes either over the top roll and through the top nip, or directly through the top nip, from which it passes to the next nip and is transferred from thence to the next lower nip, and so on, until the web passes through the bottom nip between the bottom or king roll and the roll immediately thereabove. The sliding frictional polishing action caused by the yielding of the composition rolls in its nips and by the speed differential between the surfaces of each metal roll and associated composition roll produces a high gloss on the paper. Generally, the calender stack includes a nipped pair of the composition rolls somewhat below the center of the stack, so that the surface of the paper in contact with the metal rolls below this pair of composition rolls is reversed, whereby both surfaces of the paper make contact with the metal rolls as the web passes through the calender stack. The metal rolls produce most of the polishing action on the paper, and hence it is desirable that both surfaces of the web make contact with the metal rolls.

In such a supercalender in which the bottom roll supports all of the other rolls in the stack, there is an increasing nip pressure from the uppermost nip to the bottom-most nip with the driving king roll. It is therefore quite 'difiicult to secure the same degree of finishing on both sides of the sheet in view of the fact that the pressures on the paper by the bottom rolls of the stack are greater than from the top rolls in the stack. Such high pressures also result in undue crushing of the sheet by the lowermost rolls in the stack, particularly when the stack is of a large capacity to take wide webs. In addition, the high nip pressures toward the bottom of the stack render it very diflicult to operate with a pair of relatively soft composition rolls in the bottom three or four positions of the stack, which is the preferred position of the nipped composition rolls, due to the fact that these composition rolls yield in their nips to such an extent in these positions in the stack that the paper web is unduly stressed and it thus breaks frequently. These web breakages generally mark the composition rolls, require re-threading of the web and a web splice on the roll of paper being shipped, and cause additional obvious inefficiencies. There is a differential in speed between the various rolls in the stack since each roll drives the roll just above it in the stack, and the sheet becomes very tight toward the bottom of the stack. For this reason also, the sheet tends to break as it passes through the stack, and this eifect is greater the more rolls are used in the stack and the wider the stack. The high nip pressures on the composition rolls also cause these rolls to have surface failures, which is of course undesirable. In the event of such surface failures, the composition rolls must be replaced so the sheet can be finished properly; and, for repair, the composition rolls must be resurfaced or refilled with new composition fill.

It is an object of the present invention to provide an improved supercalender in which the pressures on the paper web passing through it may be controlled both in the top part of the calender stack as well as in the bottom part of the calender stack independently, so that a more uniform finish may be obtained on both sides of the sheet solely by calender action. It is also an object of the invention to provide an improved supercalender stack in which the nip pressures are more uniform and in which the differential between the roll speeds is less pronounced so that undue failure of the composition rolls can be avoided and sheet breakages are materially reduced in frequency.

Briefly stated, the foregoing objects are accomplished in accordance with the present invention by providing a supercalender stack having a driven, axially fixed roll approximately in the center of the stack with vertically adjustable metal rolls and composition rolls disposed both above and below the driven center roll and with pressure applying mechanism being provided for both the uppermost roll and the lowermost roll in the stack for the purpose of providing the desired nip pressures between the rolls in the stack.

The invention consists of the novel constructions, arrangements and devices to be hereinafter described and claimed, for carrying out the above stated objects, and

such other objects, as will be apparent from the following description of a preferred form of the invention, illustrated with reference to the accompanying drawings, wherein:

FIG. 1 is an end elevational view of a supercalender embodying the principles of the invention; and

FIG. 2 is a side elevational view of the supercalender.

Like characters of reference designate like parts in the several views.

Referring now to the drawings, the illustrated supercalender may be seen to comprise a frame 10 having pairs of guide ways 11 and 12 provided therein. The supercalender comprises rolls 13, 14, 15, 16, 17, 18, 19, 20, 21 and 22 disposed in a vertical stack. The rolls 13, 15, 18,

20 and 22 are smooth, polished metal surfaced rolls; and

the rolls 14, 16, 17, 19 and 21 are filled or composition surfaced rolls. The rolls 1S and 20 are iron rolls which are solid except for small internal bores for water cooling or steam heating, and the rolls 13 and 22 may also be solid iron rolls with internal bores; however, preferably the rolls 13 and 22 are of the type which automatically provide uniform nip pressures between these rolls and rolls in contact with them along the complete length of the rolls, such an adjustable roll, for example, being disclosed in the patent to V. Appenzeller, No. 2,908,964, issued Oct. 20, 1959. The rolls 14, 16, 17, 19 and 21 are conventional composition surfaced rolls used in supercalenders, and each of them may comprise a solid steel core having a layer of composition disposed about and fixed to the core. The roll 14, for example, has the solid core 14a and has a cylinder 14b of composition disposed about the core and fixed thereto. The composition may be compressed cotton, for example, or other suitable materials, such as wool or asbestos. The noteworthy attribute of the outer surface portion 14b and the similar outer surface portions of the other rolls 16, 17, 19 and 21 is the yieldability of these outer roll portions as compared to the non-yieldability of the external surfaces of the associated metal rolls, providing a longer nip and a greater smoothing and ironing action on the paper passing between the rolls by the metal roll of each pair.

The center roll 18 is relatively large in diameter compared to the other intermediate rolls in the stack, and the roll 18 is rotatably carried in bearing housings 23 disposed in the guide ways 11 and 12 and fixed therein by means of keys 24. The roll 18 is driven from a motor 25 through a speed reducer 26 and a floating drive shaft 27. The other rolls 14, 15, 16, 17, 19, 20 and 21 are each provided with a bearing housing 28 which is slidably disposed between the guide ways 11 and 12. The lowermost roll 13 and the upper roll 22 are each larger in diameter than the metal rolls 15 and 20 and the composition rolls 14, 16, 17, 19 and 21, and the rolls 13 and 22 are respectively provided with housings 29 and 30 slidably disposed between the guide ways 11 and 12.

A pair of piston type cylinders 31 and 32 are provided below the bearing housings 29 for moving the roll 13 upwardly and thereby providing nip pressures between the rolls 13, 14, 15, 16, 17 and 18. The cylinders 31 and 32 are efiective on the bearing housings by means of piston rods 33 and 34. A pair of diaphragms or cylinders 35 and 36 are provided for applying a downward force on the bearing housings 30. Each of these diaphragms is connected to a swinging arm 37 which is pivoted at one end and is pivotally connected to a thrust rod 38 effective on the respective bearing housing 30. Conventional roll raising assemblies 39 and 40 are connected to the rods 38 for raising the rolls 19, 20, 21 and 22.

Paper carrying rolls 41, 42, 43, 44, 45, 46, 47, 48 and 49 are provided between opposite parts of the frame 10. A paper web A to be calendered may extend beneath the roll 41, through the nip between rolls 22 and 21, around the roll 42, through the nip between the rolls 21 and 20, around the roll 43, through the nip between the rolls 20 and 19, around the roll 44, through the nip between the rolls 19 and 18, around the roll 45, through the nip between the rolls 18 and 17, around the roll 46, through the nip between the rolls 17 and 16, around the roll 47, through the nip between the rolls 16 and 15, around the roll 48, through the nip between the rolls 15 and 14, around the roll 49, and through the nip between the rolls 14 and 13, to any appropriate winder (not shown). Each of the metal rolls, as it contacts the web passing through the calender, functions to press, smooth and iron the web and provide it with a high finish. Each of the composition rolls having a nip with a metal roll yields to some extent on its periphery and provides a longer nip and a greater polishing action on the web than would be obtainable if the composition roll were instead a metal roll. a

It will be observed that the wire side of the web A and also its felt side have been respectively marked in the FIG. 1 illustration with the designations W and F as the web A passes through the nips between the various rolls of the calender. It will be observed also that, in the upper part of the calender, the wire side of the web A is in contact with and is therefore polished by the metal rolls 18, 20 and 22 of the calender, the wire side of the web A coming into contact twice with both the rolls 18 and 20 and once with the roll 22, so that the wire side of the web has had five applications of a metal roll to it. The two composition rolls 16 and 17 have substantially less polishing action between them, and they function to reverse the web with respect to subsequent applications of metal rolls to the web; and it will be observed that the felt side of the web is polished by the lowermost two metal rolls 13 and 15 in the stack. The felt side of the web A comes into contact twice with the metal roll 15 and once with the meal roll 13, so that there thus are three applications of a metal roll to the felt side of the web as compared to five applications of a metal roll to the wire side of the web. In view of the fact that it is desirable that the wire side of a paper web be finished to a greater extent than the felt side, since the wire side is rougher, this difference in application of the metal polishing rolls to the two sides of the web A is desirable.

The calender of the invention, having its centrally located roll 18 axially stationary and rotatively driven, advantageously allows the pressures in the nips between the lowermost rolls of the stack to be substantially less than the nip pressures in the same sized stack of conventional design in which the lowermost roll is axially stationary and is rotatively driven; and the nip pressures between the rolls of my improved stack may be more uniform.

Just as an example, and referring first to a conventional supercalender consisting of ten rolls with a top roll weighing 300 pounds and intermediate rolls each weighing pounds, the force on the bottom roll of the supercalender would be 300 pounds plus 8 x 100 pounds, or 1,100 pounds, due only to the weights of the rolls. External loading applied to the top roll is added to the force each of the rolls exerts on the roll immediately below it, and the force on the bottom king roll would be 2,100 pounds if a loading of 1,000 pounds is put on the top roll. With my improved supercalender, assuming that the cylinders 31 and 32 apply an external loading force of 1,700 pounds on the lower roll 13, and that the diaphragms 35 and 36 apply an external loading of 1,000 pounds on the top roll 22, the forces at the nips between the rolls in the top part of the stack above the centrally located driving roll 18 will be 1,300, 1,400, 1,500 and 1,600 pounds, and the forces between the rolls in the bottom part of the stack below the center roll 18 will be 1,000, 1,100, 1,200, 1,300 and 1,400 pounds. It is assumed in this example also that the top and bottom rolls each weighs 300 pounds and that the smaller steel and composition rolls each weighs 100 pounds.

It thus is apparent that the nip pressures between the rolls of my improved calender are more uniform, and therefore more uniform finishing of the paper web A can be expected than using a conventional supercalender having all of the rolls supported by the bottom or king roll. Assuming that the wire side is, in general, finished by the uppermost rolls in my improved calender as illustrated, and that the felt side is finished by the lower rolls, the felt side may have approximately the same calendering pressures applied to it as the wire side so that about the same finish may be expected to both sides of the web, although, as has been explained previously, the wire side is preferably calendered to a greater extent than the felt side.

With my improved supercalender, both the lowermost roll 13 and the uppermost roll 22 may have appropriate loading put on to these rolls by the pressure applying mechanisms 31, 32, 35 and 36 in order to obtain the desired relative amount of finishing action on both sides of the web. Since the rolls above the axially fixed center roll 18, in general, finish the wire side of the web, and the rolls below the center roll 18, in general, finish the felt side of the web, the finishing to be provided on the felt side, as compared to the finishing to be provided on the wire side, may be adjusted by adjusting the loading forces on the lowermost roll 13 from the pressure applying mechanisms 31 and 32 with respect to the loading forces applied to the top roll 22 by the pressure applying mechanisms 35 and 36. It is to be understood that the wire and felt sides of the web may be provided with different finishes if desired by adjusting the pressure applying mechanisms 31 and 32 over a considerably different range than the pressure applying mechanisms 35 and 36. The calender stack may be utilized also by using only the uppermost rolls above the driving roll 18 or alternately by using only the rolls below the driving roll 18, thus operating with only 4 or 5 roll nips. This flexibility of operation, utilizing different roll combinations, allows the satisfactory finishing of various different paper grades.

Since relatively light pressures exist between the nipped composition rolls 16 and 17 and also on the composition roll 14 at the bottom of the stack, as compared to relatively heavy pressures in a conventional supercalender stack, the rolls 14, 16 and 17 are not worn unduly, due to high nip pressures. The sheet crushing that is experienced in an ordinary supercalender due to these high pressures in the lower parts of the stack also does not occur.

As has previously been explained, there is a relatively great yielding and nip extension of the relatively yieldable com-position material at the nip between two filled rolls running together, particularly under high pressures; and a paper web passing through such a high pressure nip is subjected to high stresses which tend to rupture the sheet causing inefficiencies of operation. Also, in passing through a calender, the web tends to become tight at the bottom of the stack due to greatly increasing nip pressures, which also tends to cause sheet tearing. With my improved stack, these high pressures in the bottom part of the stack have been avoided, and much less sheet breakage occurs.

I Wish it to be understood that the invention is not to be limited to the specific constructions and arrangements shown and described, except only insofar as the claim may be so limited, as it will be understood to those skilled in the art that changes may be made without departing from the principles of the invention.

What is claimed is:

A calender for a web of sheet material comprising a calender frame, a vertical stack of calender rolls held by said frame, said rolls including a driven central relatively large diameter steel roll which is axially fixed with respect to said frame and additional smaller diameter non-driven idler rolls disposed above and below said central roll and movably held by said frame to be movable toward the central roll, alternate ones of the rolls in said stack being steel and being yieldable composition surfaced except for a pair of yieldable composition surfaced rolls dis-posed in said stack which have a nip between them and one of which has a nip with said central roll, motor means for driving said central roll, and additional motor means for urging the end rolls of said stack toward said central roll for increasing the nip pressures between said rolls.

References Cited UNITED STATES PATENTS 1,423,969 7/ 1922 Schurmann. 1,575,539 3/1926 Butterworth -162 2,908,964 10/ 1959 Appenzeller 29- 116 2,926,600 3/ 1960 Engelgav 100162 X 3,016,819 1/ 1962 Kupka 100-463 FOREIGN PATENTS 665,27 2 6/ 1923 Canada.

633,101 10/ 1927 France.

295,592 12/ 1916 Germany.

463,165 3/1937 Great Britain.

OTHER REFERENCES Casey, J. P.: Pulp and Paper, 2nd ed., vol. II, N.Y. Interscience, 1960, p. 8 19.

LOUIS O. MAASSEL, Primary Examiner. 

